QuickLinks -- Click here to rapidly navigate through this document

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): ~~November~~February 2111, ~~2002~~ 2003

Synaptic Pharmaceutical Corporation
(Exact name of registrant as specified in its charter)

Delaware (State or other jurisdiction of incorporation)

Delaware (State or other jurisdiction of incorporation)		0-27324 (Commission File Number)		22-285-9704 (I.R.S. Employer Identification Number)
215 College Road, Paramus, New Jersey 07652-1431 (Address of principal executive offices) (Zip Code)

0-27324 (Commission File Number)		22-285-9704 (I.R.S. Employer Identification Number)
215 College Road, Paramus, New Jersey (Address of principal executive offices)		07652-1431 (Zip Code)
Registrant's telephone number, including area code:		(201) 261-1331

Registrant's telephone number, including area code: (201) 261-1331

(NOT APPLICABLE)
(Former name or former address, if changed since last report)

Item 5. Other Events.

On ~~November~~February 2111, ~~2002~~2003, Synaptic Pharmaceutical Corporation, a Delaware corporation (the "Company"), ~~entered~~held ~~into~~ a ~~definitive~~special meeting of stockholders. At the meeting, the Company's stockholders adopted the Agreement and Plan of Merger (the "Merger Agreement") ~~with~~dated as of November 21, 2002, among H. Lundbeck A/S ("Lundbeck"), ~~and~~ Viking Sub Corporation ("Viking Sub") and the Company. Pursuant to the Merger Agreement, at the effective time of the merger (the "Effective Time"), Viking Sub, a wholly- owned subsidiary of Lundbeck, will merge (the "Merger ~~Sub~~"), ~~pursuant~~with and tointo ~~which~~the ~~Lundbeck~~Company and the Company will ~~acquire~~become ~~100%~~a wholly owned subsidiary of Lundbeck. The Effective Time is expected to occur following the ~~capital~~expiration of the notification period under ~~stock~~Article 16 of the ~~Company~~Mexican ~~for~~Antitrust $6Law.50 ~~per~~The ~~common~~Company ~~share~~has inreceived ~~cash~~early ortermination ~~approximately~~of ~~$121 million~~the waiting period with respect to the Merger under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. The ~~per~~Company ~~share~~currently ~~merger~~anticipates ~~consideration~~that ~~represents~~the anEffective 8%Time ~~premium~~will ~~over~~occur ~~yesterday's~~in ~~closing~~March 2003, ~~price~~subject ~~and~~to athe ~~62.5% premium~~satisfaction ~~over~~or waiver of the ~~price~~closing ~~one~~conditions contained ~~week~~in ~~ago.~~the Merger Agreement.

~~Pursuant~~Under to the ~~Merger~~terms ~~Agreement,~~of the Merger ~~Sub~~Agreement, ~~will~~at ~~merge with and into~~ the ~~Company~~Effective Time (~~the~~other ~~"Merger")~~than ~~and~~shares ~~the Company will survive the Merger as a wholly-owned subsidiary~~ of ~~Lundbeck. Consummation of~~ the ~~transaction is subject to a number of conditions, including the approval of the~~ Company's ~~stockholders,~~capital ~~regulatory~~stock ~~approvals~~held ~~and~~by ~~other~~persons ~~customary~~who ~~closing~~properly ~~conditions.~~exercise ~~The~~appraisal ~~Company intends~~rights tounder ~~hold~~Delaware law): ~~a special meeting of its stockholders to approve the Merger in the first quarter of 2003 and to close the transaction shortly thereafter.~~

•: each issued and outstanding share of common stock, par value $0.01 per share, of Synaptic will be converted into the right to receive $6.50 in cash, without interest;
•: each issued and outstanding share of Series B Convertible Preferred Stock, par value $0.01 per share, of Synaptic will be converted into the right to receive $1,499.15 in cash, without interest; and
•: each issued and outstanding share of Series C Convertible Preferred Stock, par value $0.01 per share, of Synaptic will be converted into the right to receive $1,088.54 in cash, without interest.

InAt ~~connection with~~ the ~~Merger,~~close ~~Warburg~~of ~~Pincus~~the ~~Private~~market ~~Equity~~on ~~VIII,~~the ~~L.P.~~date ~~("Warburg~~of ~~Pincus")~~the ~~signed~~Effective aTime, ~~voting~~the ~~agreement~~Company's ~~with~~shares ~~Lundbeck~~of tocommon ~~vote~~stock ~~its~~will ~~shares~~be indelisted ~~favor~~from ofThe ~~the~~Nasdaq ~~transaction.~~Stock ~~Warburg Pincus~~Market ~~beneficially~~and ~~owns~~will ~~approximately~~cease ~~35%~~to ofbe ~~the Company's common stock~~traded.

~~The~~This ~~foregoing~~Current ~~description~~Report ofon Form 8-K and the press release (filed as Exhibit 99.1 hereto) contain forward-looking statements about the Merger iswithin ~~qualified~~the inmeaning ~~its~~of the ~~entirety~~Safe Harbor Provisions of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, those related to the transactions described herein and any other statements which are not historical facts. Forward-looking statements may be identified by ~~reference~~words like "expected" and "anticipates" and similar expressions. Such statements involve assumptions relating to the ~~terms~~receipt of regulatory approvals, the condition of our business and other conditions to the Merger. ~~Agreement~~Although the Company believes that the assumptions used to make the forward-looking statements contained herein are reasonable, actual facts and conditions may exist in the future that could vary materially from the assumed facts and conditions upon which issuch ~~filed~~forward-looking asstatements ~~Exhibit 2~~are based.1 ~~hereto~~Many factors, including those discussed more fully in the Company's filings with the Securities and isExchange ~~incorporated~~Commission, particularly its latest annual report on Form 10-K, as well as others, could cause results to differ materially from those stated. The Company expressly disclaims any obligation or undertaking to disseminate any updates or revisions to any forward-looking statement contained herein byto ~~reference~~reflect any change in the Company's expectations with regard thereto or any change in events, conditions or circumstances on which any such statement is based.

On November 21, 2002, the Company issued a press release with respect to the transaction described herein, which was included in a filing made by the Company pursuant to Rule 14a-12 promulgated under the Securities Exchange Act of 1934.

Each of this Report on Form 8-K and the press release contain forward-looking statements about the proposed Merger within the meaning of the Safe Harbor Provisions of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements are based on assumptions which the Company, as of the date of this release, believes to reasonable and appropriate. The Company cautions, however, that actual facts and conditions may exist in the future that could vary materially from the assumed facts and conditions upon which such forward-looking statements are based. These facts and conditions include, without limitation, that the transaction will not close on the anticipated closing date or will not close at all, if the Company's stockholders do not approve the Merger or if the Company does not receive the requisite regulatory approvals.

The Company does not undertake, and specifically disclaims, any obligation to publicly release the result of any revisions which may be made to any forward-looking statements to reflect the occurrence of anticipated or unanticipated events or circumstances after the date of such statements.

Item 7. Financial Statements and Exhibits.

(a): Financial Statements.

None.

(b): Pro Forma Financial Information.

None.

(c): Exhibits.

2.1		Agreement and Plan of Merger, dated as of November 21, 2002, by and among H. Lundbeck A/S, Viking Sub Corporation, and Synaptic Pharmaceutical Corporation.
4.1		Amendment No. 2, dated as of November 21, 2002, to the Rights Agreement, dated December 11, 1995, as amended, between Synaptic Pharmaceutical Corporation and Mellon Investor Services LLC (formerly known as Chemical Mellon Shareholder Services), as Rights Agent.
99.1		Press release dated as of November 21, 2002 issued by Synaptic Pharmaceutical Corporation.

99.1 Press release dated February 11, 2003 issued by Synaptic Pharmaceutical Corporation.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereto duly authorized.

	SYNAPTIC PHARMACEUTICAL CORPORATION
Date: February 11, 2003	SYNAPTIC PHARMACEUTICAL CORPORATION
DATE: NOVEMBER 21, 2002	By:	/s/ ERROL B. DE SOUZA Name: Errol B. De Souza Title: President and Chief Executive Officer
	By:	/s/ ERROL B. DE SOUZA Name: Errol B. De Souza Title: President and Chief Executive Officer

INDEX TO EXHIBITS

Exhibit Number
2.1		Agreement and Plan of Merger, dated as of November 21, 2002, by and among H. Lundbeck A/S, Viking Sub Corporation and Synaptic Pharmaceutical Corporation.
4.1		Amendment No. 2, dated as of November 21, 2002, to the Rights Agreement, dated December 11, 1995, as amended, between Synaptic Pharmaceutical Corporation and Mellon Investor Services LLC (formerly known as Chemical Mellon Shareholder Services), as Rights Agent.
99.1		Press release dated as of November 21, 2002 issued by Synaptic Pharmaceutical Corporation.

Exhibit Number
99.1		Press release dated February 11, 2003 issued by Synaptic Pharmaceutical Corporation.

QuickLinks

Item 5. Other Events.

Item 7. Financial Statements and Exhibits.

SIGNATURES
INDEX TO EXHIBITS

Filing Compare · SYNAPTIC PHARMACEUTICAL CORP